This invention relates to a brake vacuum booster, and more specifically, the invention relates to a vacuum booster that uses an electric actuator to improve the response time of the booster.
Brake vacuum boosters have been used extensively to increase the force applied to the master cylinder actuator when the brake pedal is applied. Vacuum boosters include a booster housing having several pressure chambers and at least one diaphragm. The diaphragm is connected to a power piston against which a primary force from the brake pedal is applied. The diaphragm also exerts a force against the power piston to supplement the force from the brake pedal. A valve is arranged between the power piston and a movable member that is connected to the brake pedal by a mechanical linkage. The member moves relative to the power piston to open and close the valve in response to brake pedal actuation. Air passages run along the movable member to provide air at atmospheric pressure to pressure chambers through the open valve, which changes the pressure differential across the diaphragm and causes the diaphragm to apply additional force to the power piston.
In an effort to increase response time of the vacuum booster when the brake pedal is applied rapidly, electric actuators have been incorporated to more rapidly open the valve and increase the force the diaphragm is able to apply on the power piston during rapid brake pedal applications. The electric actuator has been encapsulated in the movable member, which has required constructing the movable member from two components: a cylinder and a cylinder cap. Since the cylinder and cylinder cap must accommodate the air passages, it is important that they remain in alignment with one another during operation of the booster. Furthermore, the cylinder and cylinder cap are preferably used to securely retain the electric actuator within the cylinder. Previously, C- clips received in arcuate grooves in the cylinder were used, however, this arrangement permitted relative axial and rotational movement. Therefore, what is needed is a suitable cylinder and cylinder cap configuration and retaining mechanism to maintain alignment of various components and features while securely retaining the electric actuator.
The present invention provides a brake vacuum booster assembly that includes a booster housing with a plurality of chambers and a diaphragm separating the chambers. A power piston has a first passageway in fluid communication with one of the chambers, and the diaphragm is interconnected to the power piston for moving the power piston along an axis. A cylinder is at least partially disposed within a portion of the power piston and is movable along the axis relative to the power piston. The cylinder has a second passageway vented to atmosphere and in fluid communication with the first passageway. A valve is movable to an open position when the cylinder is moved along the axis relative to the power piston toward the booster housing. The valve is arranged between the first and second passageways for connecting the passageways and venting the second passageway and the one of the chambers to atmosphere when in the open position.
An electric actuator is retained within a cavity in the cylinder for coacting with the valve and moving the valve to the open position in response to an electronic request signal. A cylinder cap is connected to an end of the cylinder for retaining the electric actuator within the cavity. The cylinder cap has an opening aligned with the second passageway. A retaining mechanism is arranged between the cylinder and the cylinder cap for preventing axial and rotational movement of the cylinder cap relative to the cylinder to securely retain the electric actuator within the cavity and maintain alignment of the opening and second passageway.
Accordingly, the above invention provides a suitable cylinder and cylinder cap configuration and retaining mechanism to maintain alignment of various components and features while securely retaining the electric actuator.